#include<stdio.h>
#include<string.h>
int main()
{
	char ch[50];
	fgets(ch, sizeof(ch), stdin);
	int i = 0,count = 1;
	int len = strlen(ch);
	if((ch[0]>='a'&&ch[0]<='z')||(ch[0]>='A'&&ch[0]<='Z')||ch[0]=='_')
	{
	    for(i = 1;ch[i]!='\0';i++)
	    {
	    if((ch[0]>='a'&&ch[0]<='z')||(ch[0]>='A'&&ch[0]<='Z')||ch[0]=='_'||(ch[0]>='0'&&ch[0]<='9'))
	    {
	    	count++;
		}
		}
		if(len == count)
		printf("yes");
	    else
	    printf("no");
	}
	else
	printf("no");
	return 0;
}
